In recent years, apparatuses for transmitting and recording digital data such as music information and video information have come to be widely used in households. Since data can be recorded and read with high quality in these apparatuses, it is possible to construct a recording system in which there is no deterioration in quality even if copying is performed repeatedly. Such a recording system must include a copyright protection function to prevent copyrighted data from being illegally copied.
As such a system for the protection of copyright, for example, there is a content scrambling system in a digital video disc (DVD) ROM.
In this system, all copyrighted data on a disk is encrypted and only an apparatus which has received a license is given an encryption key for obtaining meaningful data by decrypting encrypted data. The licensed apparatus is designed to conform with operation specifications so that illegal copying may not be performed.
However, the method employed in a DVD system such as that described above is effective for ROM media, but it is not effective for RAM media in which data can be recorded by a user. The reason for this is that, in RAM media, although an unauthorized person cannot decrypt encrypted data, the person can newly create a disk which operates in an authorized apparatus by copying all the data on a disk to a new disk.